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My issue is the front end. I know Jan Diddens scaler for other software or the dedicated probe (max +/-24v) helps, but I'm used to at least 100V RMS on my AudioLab unit. I'm always on the end of high powered amplifiers and it seems only a few standalone units (AP/R&S/Panasonic/SR-1 etc) will do that.

I'm getting a QA-401 very soon (what happened to yours- did you sell it?), but it's main advantage is price and differential inputs (for BTL amps etc), but one would still need a x10 divider for it too. I'm also concerned about the rising noise floor at HF from the AK ADC. You found that to be an issue?

Even Visual Analzyer with <2V sources is a nice program, but I'm sure there's a bug in the THD+N computations as they are often below THD alone with no weighting.

In the meantime, I just use my old-skool gear Leader LDM-171 for up to 100VRMS THD+N measurements- it's indestructible.

Ricky Roma: I subscribe to the law of contrary public opinion... If everyone thinks one thing, then I say, bet the other way...

My issue is the front end. I know Jan Diddens scaler for other software or the dedicated probe (max +/-24v) helps, but I'm used to at least 100V RMS on my AudioLab unit. I'm always on the end of high powered amplifiers and it seems only a few standalone units (AP/R&S/Panasonic/SR-1 etc) will do that.

I'm getting a QA-401 very soon (what happened to yours- did you sell it?), but it's main advantage is price and differential inputs (for BTL amps etc), but one would still need a x10 divider for it too. I'm also concerned about the rising noise floor at HF from the AK ADC. You found that to be an issue?

Even Visual Analzyer with <2V sources is a nice program, but I'm sure there's a bug in the THD+N computations as they are often below THD alone with no weighting.

In the meantime, I just use my old-skool gear Leader LDM-171 for up to 100VRMS THD+N measurements- it's indestructible.

Yes I sold the QA401. At signal levels below about -20 dBFS the noise floor was good, maybe -150dbFS with 32k FFT, but as you approach 0dBFS it would rise to around -125 dbFS. It really depends what you are doing whether this is an issue for you, but I want to look closely at the low level spuria going on. My motu will manage this. The distortion would be obscured with the 401.

That's one thing I wonder about with those differential input, where can you get adapter cables to convert XLR to differential BNC? I saw something like this for a Keysight analyzerhttp://literature.cdn.keysight.com/litweb/pdf/5991-0435EN.pdf
Also, how do you connect single ended RCA outputs to the differential BNC? Do you just connect to one, or do you split, connecting to the + and -?

Major Contributor

That's one thing I wonder about with those differential input, where can you get adapter cables to convert XLR to differential BNC? I saw something like this for a Keysight analyzerhttp://literature.cdn.keysight.com/litweb/pdf/5991-0435EN.pdf
Also, how do you connect single ended RCA outputs to the differential BNC? Do you just connect to one, or do you split, connecting to the + and -?

Active Member

B Series APx555 High-Performance Audio Analyzer
The arrival of the B Series APx555 audio analyzer brings several enhancements to the analog high-performance sine generator that will have broad appeal to developers of high-performance audio devices such as compressors, limiters, amplifiers, codecs and digital signal processors. This enhanced analog generator (EAG)—standard with B Series APx555 analyzers and available as an upgrade for Legacy APx555 systems—provides several improvements in its low distortion sine generator and high-precision sine analyzer, including improved sine generator frequency stability with an accuracy of <30 ppm. The system can now also generate low-distortion analog sine burst signals from 5 Hz to 100 kHz and allows users to independently invert the signal polarity of balanced channel outputs. Finally, the B Series APx555 has lower system residual distortion, with THD+N improvement above 50 kHz (−2 dB) and THD improvement above 5 kHz (varying from −2 to −5 dB).